Tornado Shape After Poly-Si Wet Etching

Tornado Shape After Poly-Si Wet Etching

Material Name: Silicon
Record No.: 96
Primary Chemical Element in Material: Si
Sample Type: Wafer
Uses: Etching
Etchant Name: None
Etching Method: Wet etching
Etchant (Electrolyte) Composition: No data
Procedure (Condition): No data
Note: The reason there are Si residues is largely divided into two categories. One is low wettability by hydrophobic Si surface and the other one is local residues due to insoluble H2 Bubbles that are generated during a wet etching. At First, as shown in Figure 1, The shape of the defect inspection map appears like a tornado that is generated by a poor wetting, the cause of this occurrence is as follows. Before Si etching, a pre-treatment of Fluorine series is needed to remove native oxide. As a result, Poly-si is significantly changed to more hydrophobic. In this state, Alkali solutions cannot be used fully when wetting on the wafer’s surface, and it makes tornado shaped defects in the single type equipment. This problem can be solved using a hydrophilic surface treatment(SC1) between fluorine pretreatment and poly-si wet etching. This can be demonstrated via the contact angle measurement, surface tension of the solution is dramatically reduced by SC1 treatment. Additionally, we have learned that the solutions having longer carbon chains have better wettability than ammonia and small amounts of IPA with a low surface tension added for improving wettability.
Reference: Kihyung Ko, et al., A study on the removal method of Si residue during Si Wet Etch, Abstract #2102, 224th ECS Meeting, 2013 The Electrochemical Society, pp. 1.

Figure 1: Defect inspection map of tornado shape after poly-si wet etching & SEM image of poly residue.